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HTTP caching headers

What is the Age header?

Age is the number of seconds since the origin generated or revalidated a response. A cache sets it; 0 or no Age usually means it came from origin.

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Age is an HTTP response header, set by caches, that gives the number of seconds since the response was generated or last revalidated by the origin. A downstream cache compares it with `max-age` to work out how much freshness is left. A response straight from the origin usually has no Age or Age: 0.

HTTP/1.1 200 OK
Cache-Control: max-age=3600
Age: 1250

This response has 2350 seconds of freshness left for the next cache that stores it. Age is a clue, not a verdict. A `Cache-Status` or vendor header says directly whether the response was a hit or a miss.

  • With tiered caching, a hit at an edge can carry an Age inherited from an upper tier. Cloudflare documents this, so Age can be older than the last local fill.
  • Cloudflare sets Age on HIT, STALE and UPDATING responses, and not on MISS, DYNAMIC or BYPASS.

Related terms

References

  1. RFC 9111: HTTP Cachinghttps://www.rfc-editor.org/rfc/rfc9111
  2. MDN: Agehttps://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Age
  3. Cloudflare: Cache responseshttps://developers.cloudflare.com/cache/concepts/cache-responses/

Warm your cache after every deploy

sitewarm requests the pages in your sitemap after a deploy and reports the cache state the CDN returns for each one, with the vantage point it was measured from.

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